492 BELL SYSTEM TECH SIC AL JOl'RX.IL 



decline than is the lower frequency. During the summer time, 

 afternoon reception in England is belter on the higher frequency 

 channel. This is Ijecause of the considerably greater static exper- 

 ienced at this time on the lower frequency. The higher signal-to- 

 noise ratio prevailing during the winter month of January as com- 

 pared with the summer month of July is evident. This is due primar- 

 ily to higher summer static. 



Seasonal Variation in Eni^land and United States. 1-Or the 57- 

 kilocycle channel there is shown in Fig. 20, for each month of the 

 year, signal-to-noise ratios of two years' data. These show a distinct 

 dip corresponding to the sunset dip of the signal field strength. The 

 night-time values arc generally high in accordance with the high 

 night-time signal strength but the maximum values are shifted toward 

 the lime of sunrise. This is due to the fact that the noise rises earlier 

 in the afternoon and declines earlier in the indiniiig than do the cor- 

 responding variations in signal slrengiii. 



Fig. 27 presents the signal-to-noise ratios for such data as have 

 thus far been obtained upon transmission from England to the I'nited 

 States on a frequency of .52 kilocycles. The low values obtained 

 about sunset are, of course, due to the evening dip in field strength. 

 In general, the night-time ratios do not reach high values as do those 

 for England because the early morning signal field strength begins 

 to fall off while the noise level is still high. Comparisons of the 

 signal-to-noise ratios obtained at New Southgate and at Belfast 

 show that the Belfast values are somewhat higher for that part of 

 the day, corresponding to forenoon in the United States and after- 

 noon in England. This is because the forenoon static in the United 

 States is lower than the afternoon static in England. 



DlRIiCTIVK RliCKIVI\(, AnthnnaI'; 



The |)icture whicli has been gi\en of the transmission of static 

 northward from the tropical lielt suggests that the signal-to-noise 

 ratio might be materially' improved by the use of directional receiving 

 systems. This is, of course, what has actually been found to be 

 the case in commercial transatlantic radio telegraphy wherein the 

 Radio Corporation has made such effective use of the wave antemia 

 devised by Be\erage. The expectations are confirmed by measure- 

 ments which have been made in the |)resent experiments using sucii 

 wave antennae. 



A year and a half ago the British Post Office established a wave 

 antenna with which to recei\e from the Rocky Point radio telephone 



